1. Field of the Invention
The present invention relates to high-pressure, high-temperature presses, and more particularly to locking mechanisms for high-pressure, high-temperature presses.
2. Background
Over the course of the last fifty years, ultra high-pressure, high-temperature (HPHT) presses have been developed to produce superhard materials. Superhard materials may include, for example, diamond, polycrystalline diamond, ceramics, cubic boron nitride, or exotic metalloid gases such as metallic hydrogen. To create these materials, these presses must often exert payload pressures in excess of 35 kilobars while applying temperatures of 1000 degrees Celsius or more.
One of the original designs for an HPHT press was invented by Dr. H. Tracy Hall in the 1950s and is disclosed in U.S. Pat. No. 2,918,699, which is herein incorporated by reference for all that it contains. This design utilizes a tie-bar frame supporting several hydraulic piston cylinders to exert pressure on a centrally located payload. Because the bending moments of the tie-bar press are so great, the tie-bar press becomes enormous as the size of the press is increased. For example, the weight of a 3000-ton tie bar press may exceed sixty tons due to the force exerted by the hydraulic cylinders. By comparison, the weight of a 4000-ton tie-bar press may increase to over one hundred tons. Nevertheless, despite this enormous size, the bending moments of a 4000-ton tie-bar press are great enough that the tie-bar frame still experiences occasional fatigue failures.
More recently, an HPHT press was invented by David R. Hall which utilizes a reduced-mass unitary frame, which is disclosed in U.S. Pat. No. 6,336,802, which is herein incorporated by reference for all that it contains. The unitary frame is constructed of a high strength material, such as high-strength steel, and comprises intersecting cylindrical openings where several hydraulic cartridges are inserted and attached, such as by screwing the hydraulic cartridges into the openings. These hydraulic cartridges may be used to exert huge forces on a payload located at or near the center of the unitary frame. Due to its unique design, a 3000-ton press using the unitary frame may, in certain embodiments, weigh less than 12 tons. This provides a significantly better weight-to-capacity ratio compared to the tie-bar press described above.
More recently, an improvement to the unitary frame design was disclosed in U.S. patent application Ser. No. 11/175,238 directed to “Strain Matched Threads for a High Pressure High Temperature Press Apparatus”, also invented by David R. Hall et al. That application discloses the use of tapered threads to mate the hydraulic cartridges to the openings of the unitary frame. It is believed that the by choosing a proper angle for the tapered threads, the reaction forces of the press are distributed substantially equally across the threads. The tapered-thread design may also reduce fatigue or cracking of the hydraulic cylinders by roughly equalizing, or at least reducing the great disparity between, the stiffness of the hydraulic cylinders and the unitary frame. U.S. patent application Ser. No. 11/175,238 is also herein incorporated by reference for all that it contains.
Moreover, because of the taper angle, number of threads, and coarseness of the thread form, the hydraulic cartridges may only require about three complete turns for all the threads to fully engage. The tapered threaded connection is thus a more efficient design that makes assembly and repair of the press apparatus significantly quicker than the non-tapered unitary frame design, which required as many as fifteen complete rotations for the threads to seat. Consequently, the tapered-thread design may be about five times quicker to assemble than previous non-tapered designs. Additionally, thread damage due to accidental cross-threading during make up of the hydraulic cartridge and unitary frame is substantially reduced using tapered threads. Finally, tapered threads increase the thread surface area, thereby providing excellent pull-out resistance.
Nevertheless, tapered threads may also be prone to unscrew upon applying pull-out pressure. This is potentially dangerous in an HPHT press and may cause thread damage to the hydraulic cylinder or the unitary frame. Thus, apparatus and methods are needed to prevent a tapered threaded connection from unscrewing. Further needed are apparatus and methods for finely adjusting the threaded connection to ensure that the tapered threads seat properly.